Field of the Invention
Embodiments of the present invention relate, in general, to sporting equipment and more particularly to a laterally-sliding skateboard truck assembly.
Relevant Background
The modern skateboard comprises several basic components, including a riding surface (a deck or board), usually made of an elongated piece of wood, fiberglass or some other sturdy, resilient and flexible material; four wheels, having some sort of ball-bearing arrangement upon which the deck and rider are transported; and two skateboard “trucks”, wherein the trucks are the steering mechanisms or devices by which the wheels are connected to the deck. Generally, the trucks are attached to the deck in a mirror-image manner, such that as a user leans to one side of the skateboard, the forces applied by the user cause each truck to simultaneously steer opposite one another. For example, as the rider leans left, the front truck (“front” being the general direction of motion) turns left while the rear truck turns right, forming a leftward arcing path along which the rider travels. While located in a fairly unobtrusive location on the underside of the deck, the trucks on which the wheels are suspended are very important, as the trucks determine how the skater controls the skateboard.
In modern skateboards, the truck includes a base plate, or mounting plate, which is used to screw or bolt the truck to the bottom of the deck; a bolt, which attaches a wheel-mounting axle to the base plate; and an upward-projecting, wheel-mounting axle. The axle suspends the skateboard wheels on either side of a kingpin.
The turning ability of the skateboard depends on the design and adjustments made to the kingpin, as the wheels of the skateboard traditionally pivot around or in close proximity to the kingpin. The kingpin is generally threaded through an oversized hole lined with compressible and resilient bushings, often made of plastic components such as urethane, whereby tightening the kingpin makes it more difficult to flex the axle, and therefore more difficult to turn the skateboard (tightening the kingpin also generally tends to make the skateboard more stable, so there is an inherent trade-off between a user's desire for skateboard maneuverability and stability at high speeds).
As the user leans from side to side, the bolt presses against the bushings, enabling turning and at the same time compressing against the bushings, such that further leaning becomes more and more difficult for the user because of the force of the bushings. The skateboard user steers the skateboard by leaning from one side to another, thereby applying pressure to the truck, such that the truck pivots around the kingpin so that on the front wheels, the outer wheel moves forward while the inside wheel moves aft; on the rear wheels, however, the outer wheel moves aft and the inner wheel moves forward, the resultant forces causing the two sets of wheels no longer to be in alignment. Rather, the wheel sets describe an arc through which the skateboard now travels.
Snowboarding was initially developed as a way to blend surfing and skiing, just as skateboarding was developed as a blend of surfing and skating. Skateboarders appreciated the lateral movement possible in snowboarding and skiing and began to try to obtain similar movement on their skateboards. Much of the popularity of snowboarding rests in its seductive freedom of movement. While these movements result from complex interactions between the board, rider and snow conditions, at least two general characteristics can be readily identified.
First, a snowboarder can turn by leaning his or her weight towards the intended direction of travel. The effect results from the presence of “sidecut” (that is, the concave arc segment of the board's midsection) and flex of the board design. As the board leans onto its edge, it turns along an arc formed by the board's edge; the more deeply concave the edge of the board, the smaller the circle traced by the tighter arc. The radius of this circle is known as the “sidecut radius”. If this type of turn is executed cleanly—that is, with little-to-no lateral slippage (also known as “skidding”)—it is referred to as “carving”. In addition to shortening the sidecut radius, the rider can also control the severity of the turn radius by varying the degree of the lean.
Skateboarders have long replicated this type of carving behavior through the mechanical design of the skateboard trucks. Prior art truck designs turn the skateboard through gentle or severe turns, depending on the amount of lean, much like a snowboard.
Another motion characteristic of a snowboard is its ability either to slide or skid. “Sliding” occurs when the board moves along its longitudinal axis, while lateral motion is typically referred to as “skidding”—as when a car skids while attempting to turn on a slick surface. By adjusting the rider's weight on the board, the board can skid forward, backwards or sideways in the direction of travel. This type of lateral motion varies in inverse proportion to the functioning of the board's edges to carve cleanly through the snow (as opposed to relaxing their “grip”, resulting in “skidding”), enabling the rider to experience full omnidirectional motion.
These numerous similarities between snowboarding and skateboarding have led each sports industry to attempt to improve its products by creating or redesigning them to include features found to be useful in the other sport. One of the most significant modifications to the skateboarding industry has been the attempt to redesign a skateboard configuration to include one or more features prevalent in snowboarding, to include the introduction of lateral motion for increased maneuverability and speed control, as well as the ability to perform tricks, such as a 360-degree spin.
A laterally-sliding board, also known as a “Freeboard”, is a specialist skateboard designed to closely emulate the behavior of a snowboard. Freeboards were initially developed to allow snowboarders to transition to skateboarding (as an off-season sport), without the need to adapt to a smaller deck and narrower wheelbase.
A freeboard typically has 6 wheels: Four normal, longboard-style wheels at each corner, and two center wheels. The center wheels are often spring-biased but are allowed to caster in all directions. The ability of the wheels on the center axis to freely turn in all directions enables the board to “slide” laterally, provided that neither of the two downhill, corner wheels contact the ground. This mimics the traditional “side-to-side” motion of snowboard riding. By exerting pressure on the corner wheels, the rider is able to control the board.
While these boards were an alternative to the traditional skateboard, permitting “drifting” or “sliding”, the suspension system for the wheels, that is, the “truck”, was a heavy, unarticulated, solid piece of metal, with one or more casters placed at the center of the truck, with the outer wheels mounted on a single “hangar” (axle assembly), as well as one or more casters placed on the center side of the truck. The hangar and caster(s) were all affixed to a single truck, with one truck on either end of the board. Thus, when a rider wanted to slide the board, the wheels on the uphill edge of the board would rotate closer to the deck at the same angle as the wheels on the downhill edge of the board would rotate closer to the ground. The precariousness of this arrangement limits the clearance distance of the downhill wheels with the ground, making it dangerous for riders: If the downhill wheels contact the ground, they can “catch an edge” (analogizing to the similar term in snowboarding) severely decelerating or stopping the skateboard, and throwing the rider from the skateboard. This is similar to a snowboarder catching an edge, albeit on concrete rather than snow.
When a rider wanted to slide the board, once the rider overcame the initial inertia and forced the castering wheels to turn enough to lift the downhill wheel off the ground and force the castering wheels to turn in the direction of the “drift”, or “slide”, only the castering and uphill wheels remained on the ground. The downhill, non-castering wheels remained dangerously close to the ground: Even a minor irregularity in a street's surface could “catch” one or more downhill wheels and send the skateboarder flying off the skateboard and onto the pavement. The precariousness of this arrangement can be seen not only in videos of riders on these types of boards—the riders shown delicately trying to balance the sliding motion with two of the six wheels on the skateboard only a few millimeters above the rough pavement—but also in the fact most of these boards are sold with bindings that enhance stability by keeping the rider's feet firmly attached to the skateboard.
A biased caster was developed for more positive control over the laterally-sliding rollerboard. The center caster was connected to a spring and biased through spring-loading to align with the longitudinal board axis, and the rider had to overcome the spring's threshold force, or moment, so the caster wheel would caster to move the board laterally. Snowboards have a natural tendency to go straight and biased casters were designed to simulate that tendency.
More recently, a cam system was introduced, in which the position of the caster wheel was displaced laterally from the board's longitudinal centerline as the board was placed into a slip or skid. Cam linkage between the side wheels and the center wheel moved the center wheel laterally as a lateral slide was initiated and returned it to a neutral, longitudinally-centered position when the board was traveling along the longitudinal board axis.
A long-felt need exists for a safer, laterally-sliding board suspension system that allows for smooth, controlled slides, drifts and stops. This system would allow the uphill wheels and the center castering wheel to remain on the ground while the downhill wheels are lifted off the ground to a clearance height sufficient to avoid the pavement or surface irregularities. Moreover, a strong need remains for a wheel assembly that is stable for all skill levels, so that even inexperienced riders can learn techniques associated with drifts, slides and stops—but at their own pace and in an environment (and speed) that enhances rider safety. A need also exists to allow riders to customize their boards to suit their riding preferences for the position and characteristics of the center wheel and fixed-wheel configurations. Lastly, freeboards of the prior art operate in a “rocker” fashion, in which the board, when resting on the center wheel, must tip to one side or the other for the fixed wheels on that side of the board to contact the pavement. This functioning is necessary for prior-art boards to “slide” laterally, but is unlike that of a snowboard, which has no rocker-like operation, and the rickety, spasmodically-alternating, left-lean-right-lean, rocker-like motion of these boards is very disconcerting to novice riders. These and other deficiencies of the prior-art designs are addressed by one or more embodiments of the present invention.
Additional advantages and novel features of this invention shall be set forth in part in the description that follows, and will become apparent to those skilled in the art upon examination of the following specification or else may be learned by the practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities, combinations, compositions and methods particularly pointed out in the appended claims.